The present invention relates to a joining or bonding method and apparatus for fusing and agitating a metal member such as castings or a plate material by friction.
According to a conventional joining technique, plate materials, or metal members each press-molded in advance into a three-dimensional shape, are overlaid on each other, and are joined with each other by electrical resistance welding, arc welding, an adhesive, bolt fastening, rivets, or the like.
When the metal members have complicated three-dimensional shapes, spot welding that can locally join a plurality of discrete joining portions is used.
According to another joining technique, a joining method of performing frictional agitation in an unfused state is disclosed in Japanese Patent No. 2712838. According to this joining technique, a projection called a probe is inserted and translated, while being rotated, into a joining surface formed by abutting two members against each other. The metal textures in the vicinity of the joining surface are plasticized and joined by frictional heat.
Japanese Patent Laid-Open Nos. 10-183316 and 2000-15426 disclose a surface treating method in surface treating castings such as a contact surface of a cylinder head with respect to a cylinder block. According to this method, a rotary tool with a projection formed at the shoulder of its distal end is pressed into the casting while being rotated, so that agitation is performed when the casting is not fused by heat.
Frictional agitation joining in the unfused state described above has the following problems. The rotational speed and pressure of the rotary tool cannot be increased very high. As the area of that receiving surface of a stationary tool which abuts against the member is larger than that of the projection projecting from the distal end of the rotary tool, the pressure is dispersed over the entire surface of the receiving surface. The frictional heat generated by rotation of the rotary tool is dissipated over the entire surface of the receiving surface. Consequently, joining takes time.
Therefore, if the rotational speed of the tool, forcing amount of the tool, traveling speed of the tool, and the like are increased more than necessary, joining may become incomplete, or the joined portion may be undesirably fused. Hence, to shorten the joining time is limited.
According to the above conventional joining technique, control parameters such as rotational speed and forcing amount of the tool which are optimal for the thickness or material of the member are obtained in advance by an experiment or the like. When members different from those in the conventional case are to be joined due to a design change, optimal control parameters must be obtained again by an experiment or the like. Quality evaluation for the joining strength and the like is performed through a tensile test or the like by using a sample formed by actual joining. This requires a separate inspection process.
Therefore, if quality evaluation of actually joined members can be performed along with joining by using control parameters, quality evaluation of the members can be performed each time joining is performed. Thus, mass production can be coped with appropriately. Furthermore, when members different from those in conventional members are to be joined due to a design change, optimal control parameters can be calculated easily. This is very effective in improving the yield by suppressing defective products.
However, no system that evaluates the quality as described above in frictional agitation joining has been developed yet.
The present invention has been made in view of the above problems, and has as its object to provide a joining method and apparatus using frictional agitation, with which heat dissipation from the joined portion is suppressed and the joining time is shortened, so that the joined state can be stabilized.
It is another object of the present invention to provide a joining method and apparatus using frictional agitation, with which the joined state of members can be managed along with joining, so that a separate inspection process is not necessary.
In order to solve the above problems and to achieve the above objects according to the present invention, a joining method using frictional agitation of rotating a rotary tool which has a first tool portion and a second tool portion with an area smaller than that of the first tool portion and projecting from a distal end of the first tool portion, overlaying first and second members with each other, and performing agitation with friction, thereby joining the first and second members, comprises urging and pressing the rotary tool into the first member from the second tool portion while the rotary tool is being rotated, cutting the member around the rotary tool by rotating the rotary tool in the member into which the rotary tool has been pressed, fusing the cut member by agitation by the first tool portion with friction in the member, and extending the region to be fused to the second member to join the first and second members to each other.
When compared to conventional welding, a current and the like required for welding become unnecessary, so the joining time can be shortened.
Preferably, when joining is ended, the rotary tool is retracted in a rotating state from the members. Thus, the joined portion is cooled after that, and joining is completed.
Preferably, a stationary tool is arranged to oppose the rotary tool so that the first and second members are sandwiched by the stationary tool and rotary tool and such that a separation distance with respect to the rotary tool can be changed, and that distal end of the stationary tool which opposes the rotary tool is formed to have substantially the same area as that of a distal end of the second tool portion of the rotary tool. Thus, heat dissipation from the joined portion is suppressed, the joining time is shortened, and the joining strength can be increased.
Preferably, the joining method further comprises the joining management step of detecting a heat generating state of the members during joining, detecting a forced state of the rotary tool with respect to the members, detecting a joined state of the members from the heat generating state and forced state, and checking whether the joined state of the members is good or not from the joined state. Thus, the joined state of the members can be managed during joining, so a separate inspection process becomes unnecessary. Whether the members are joined well or not can be managed by using control parameters used during joining.
Preferably, a generated heat amount of the heat generating state is calculated on the basis of a coefficient of kinetic friction of the members and a load acting on the members, and a forcing amount of the forced state is calculated on the basis of an encoder output of a motor that vertically moves the rotary tool with respect to the members. Thus, the joined state of the members can be managed by using control parameters used during joining.
According to the present invention, a joining apparatus using frictional agitation of rotating a rotary tool which has a first tool portion and a second tool portion with an area smaller than that of the first tool portion and projecting from a distal end of the first tool portion, overlaying first and second members with each other, and performing agitation with friction, thereby joining the first and second members, comprises tool control means for urging and pressing the rotary tool into the first member from the second tool portion while the rotary tool is being rotated, cutting the member around the rotary tool by rotating the rotary tool in the member into which the rotary tool has been pressed, fusing the cut member by agitation of the first tool portion with friction in the member, and extending the region to be fused to the second member to join the first and second members to each other.
When compared to conventional welding, current and the like required for welding become unnecessary, so the joining time can be shortened.
Preferably, a stationary tool is arranged to oppose the rotary tool so that the first and second members are sandwiched by the stationary tool and rotary tool and such that a separation distance with respect to the rotary tool can be changed, and that distal end of the stationary tool which opposes the rotary tool is formed to have a sectional area smaller than at least that of a first tool portion of the rotary tool. Thus, heat dissipation from the joined portion is suppressed, the joining time is shortened, and the joined state is stabilized.
Preferably, the distal end of the stationary tool has substantially the same area as that of a distal end of the second tool portion of the rotary tool, and the stationary tool is formed such that the closer to a counter rotary tool side away from the distal end of the stationary tool, the larger the sectional area. When the distal end of the stationary tool wears, it can be cut and be used again.
Preferably, the distal end of the stationary tool forms a curved surface. Thus, stress concentration to the members and the sink can be decreased. Even if the angle with which the stationary tool abuts against the members slightly differs, the stationary tool is received by a surface and not by a point or line. Therefore, variations in joining strength can be suppressed, and a stable joining quality can be assured easily.
Preferably, the first tool portion has a shoulder which is concentric and with a decreasing diameter from the first tool portion toward the second tool portion so as to form a step. Thus, three or more overlaid members or members with a large total plate thickness can be joined.
Preferably, the joining apparatus further comprises a joining management unit comprising generated heat detection means for detecting a heat generating state of the members during joining, forced stated detection means for detecting a forced state of the rotary tool with respect to the members, joined state detection means for detecting a joined state of the members from the heat generating state and forced state, and checking means for checking whether the joined state of the members is good or not from the joined state. Thus, the joined state of the members can be managed during joining, and a separate inspection process becomes unnecessary.